As phase-change materials such as Ge2Sb2Te5 (GST) undergo dramatic changes in material properties due to a fundamentally local change in bonding behavior, the ultimate speed limits of the atomic switching process offer hope both for ultrafast switching as well as non-adiabatic energy efficient routes for memory applications [1, 2]. To this end, we have carried out experiments using the freeelectron laser SACLA to explore sub-picosecond lattice dynamics in epitaxial GST (111) in response to 30 fs optical pump excitation. The SACLA x-ray beam was used to probe the lattice dynamics using a symmetric diffraction geometry.